Instantiate DefaultDOTGraphTraits

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90133 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/opt/GraphPrinters.cpp b/tools/opt/GraphPrinters.cpp
index 1ae6be2..2eeac3d 100644
--- a/tools/opt/GraphPrinters.cpp
+++ b/tools/opt/GraphPrinters.cpp
@@ -46,6 +46,9 @@
 namespace llvm {
   template<>
   struct DOTGraphTraits<CallGraph*> : public DefaultDOTGraphTraits {
+
+  DOTGraphTraits (bool isSimple=false) : DefaultDOTGraphTraits(isSimple) {}
+
     static std::string getGraphName(CallGraph *F) {
       return "Call Graph";
     }